Karadzic was halfway down the 3.2-kilometre-long stretch from the cave's entrance to the cavern in which twelve boys and their football coach have been trapped since June 23rd.
The group became trapped in the Tham Luang cave network after becoming flooded in while visiting after football practice.
Four of the boys were successfully brought out of the cave on Sunday. The rescue operation is ongoing.
“It was a huge success,” Karadzic told Ritzau via telephone of Sunday's operation.
“We had imagined all sorts of catastrophic situations – equipment breaking, children panicking and needing to be resuscitated.
“We were prepared for that, but it didn't happen. Everyone was on the spot and did their jobs exactly,” he said.
The Danish diver, who owns a diving company on the island of Koh Tao, has participated in the rescue operation as a volunteer since last week. He said his role on Sunday was to help provide replacement air tanks for the divers who brought the boys up from the cave.
The five-hour journey out of the cave system contains a number of passages that are not flooded. Karadzic and other divers prepared for the operation by placing cylinders in these areas, he told Ritzau.
On Friday, diver Saman Kunan, a former Thai navy seal, died from a lack of air while replenishing air tanks in one of the chambers, starkly illustrating the perilous nature of the operation.
The four boys who were rescued on Sunday “looked a bit scared, but weren't panicking or anything,” Karadzic said.
Eight boys, along with their adult football coach, are still trapped at the time of writing with the rescue mission continuing on Monday.
Karadzic said he would not be involved on Monday, but could return at a later stage.
“I'm more tired than I've ever been before and have been told to relax,” he said.
The Danish diver said he hoped “four or five” of the boys could be brought back to the surface on Monday.